The following abbreviations are herewith defined, at least some of which are referred to within the following description of the prior art and the present invention.
AWG Arrayed Waveguide Grating
CMOS Complementary Metal-Oxide-Semiconductor
FTTB/C Fiber-to-the-Building/Cabinet
FTTH Fiber-to-the-Home
IRZ Inverted Return to Zero (modulation)
LoC Laser-on-CMOS
ONU Optical Network Units
PON Passive Optical Network
Rx Receiver
RZ Return to Zero (modulation)
PIN Positive Intrinsic Negative (photo detector)
TDM Time Division Multiplexing
TRx Transceiver
TTF Thin-Film Filter
Tx Transmitter
VCSEL Vertical Cavity Surface Emitting Laser
WDM Wavelength Division Multiplexing
It has long been anticipated that conventional integrated electrical circuits (chips) based on CMOS (complementary metal-oxide-semiconductor) will eventually contain light emitting transmitters. This highly desired function, being part of the wider silicon photonics area, would remove the bottle-neck of chip-to-chip communication resulting from electrical signaling, which is limited in distance and bit-rate.
Recently, several research groups, both from universities and device manufacturers have demonstrated various ways of enabling light generation with CMOS compatible materials. The most promising approaches for low cost and direct integration of light emitting transmitters on CMOS chips, involve producing lasers directly on silicon. See, R. Chen, et al. “As-Grown InGaAs Nanolasers for Integrated Silicon Photonics”, PDIWI2, Photonics in Switching, Monterey, 2010 (the contents of this document are incorporated herein by reference). This way, conventional fiber optics could be attached to the CMOS chip (e.g., laser being part of the chip package) hence enabling flexible chip-to-chip communication on the same board, between boards, between chassis etc. This concept could be termed Laser-on-CMOS (LoC).
The above envisioned LoC would enable extreme flexibility and low cost in short reach communications or intra-site communications (i.e. chip-to-chip, board-to-board, system-to-system) over parallel fibers for full duplex communication between optical ports. In these types of intra-site communications it may be desirable to reduce the number of fibers used since more fibers means more connectors and in general more cost due to the handling of fibers and the space taken-up by the fibers. Hence, there is a need to enable intra-site communications where only one fiber instead of parallel fibers are used for full duplex communication between optical ports. This need and other needs are satisfied by the present invention.
In another application which involves longer reach communications or inter-site communications (i.e., between buildings, central offices, data centers) there is typically a limited number of fibers that are available between the sites. Thus, wavelength division multiplexing (WDM) is often utilized to fit more channels into the same fiber. However, if the above envisioned LoC is used in this application then this would require the LoC to be WDM-capable. This requirement would firstly much complicate and increase the cost of such LoC chips as well as limit the flexibility as the color of each laser would have to be pre-determined. Techniques involving the use of tunable lasers exist but it is also likely to increase the complexity and cost. Hence, there is a need to enable inter-site communications where the LoC is WDM-capable but without the aforementioned shortcomings associated with the increased cost, the increased complications, and the limited flexibility. This need and other needs are satisfied by the present invention.